The Avon Longitudinal Study of Parents and Children - A resource for COVID-19 research: Home-based antibody testing results, October 2020

Abstract

The Avon Longitudinal Study of Parents and Children (ALSPAC) is a prospective population-based cohort study which recruited pregnant women in 1990-1992 and has followed these women, their partners (Generation 0; G0) and offspring (Generation 1; G1) ever since. The study reacted rapidly to the COVID-19 pandemic, deploying online questionnaires in March and May 2020. Home-based antibody tests and a further questionnaire were sent to 5220 participants during a two-week period of October 2020. 4.2% (n=201) of participants reported a positive antibody test (3.2% G0s [n=81]; 5.6% G1s [n=120]). 43 reported an invalid test, 7 did not complete and 3 did not report their result. Participants uploaded a photo of their test to enable validation: all positive tests, those where the participant could not interpret the result and a 5% random sample were manually checked against photos. We report 92% agreement (kappa=0.853). Positive tests were compared to additional COVID-19 status information: 58 (1.2%) participants reported a previous positive test, 73 (1.5%) reported that COVID-19 was suspected by a doctor, but not tested and 980 (20.4%) believed they had COVID-19 due to their own suspicions. Of those reporting a positive result on our antibody test, 55 reported that they did not think they had had COVID-19. Results from antibody testing and questionnaire data will be complemented by health record linkage and results of other biological testing– uniting Pillar testing data with home testing and self-report. Data have been released as an update to the original datasets released in July 2020. It comprises: 1) a standard dataset containing all participant responses to all three questionnaires with key sociodemographic factors and 2) as individual participant-specific release files enabling bespoke research across all areas supported by the study. This data note describes the antibody testing, associated questionnaire and the data obtained from it.

Bias from questionnaire invitation and response in COVID-19 research: an example using ALSPAC

“…Additional linkage data -such as from Public Health England COVID-19 testing data -or data from other sources is required to answer such questions 39 . For instance, recent research using ALSPAC COVID-19 serology test data demonstrates that individuals consenting to have a COVID-19 antibody test were more likely to report having had COVID-19 23 . Questionnaire completion may have been similarly biased, thus increasing the risk of selection bias in studies where COVID-19-related outcomes are the outcome of interest.…”

“…Since the start of the pandemic, participants have been sent four online COVID-19 questionnaires to assess diagnoses, symptoms, and behavioural and environmental factors related to COVID-19, and the impact of the pandemic on health 19,20,23,24 . Questionnaires were sent to all participants who had not withdrawn from the study or declined to participate in questionnaires, and had a valid email address in the ALSPAC administrative records.…”

The Avon Longitudinal Study of Parents and Children - a resource for COVID-19 research: approaches to the identification of cases November 2020

“…Antibody tests provided by Una Health and Fortress Diagnostics Ltd. were sent to consenting participants in October 2020. The methodology is described in more detail here 7 . Briefly, 5220 participants were sent testing kits through the reporting a positive result on our antibody test, 55 reported that they did not think they had had COVID-19 in Q3, emphasising the importance of not relying on symptoms and self-report only.…”

“…Self-report data Online questionnaires were completed by participants in March (Q1), May (Q2) and October 2020 (Q3) [5][6][7] . The following questions were asked: Using [1] we applied the algorithm developed by Menni et al 10 for each set of monthly data to determine whether a participant was a 'probable' case in that month 11 .…”

The Avon Longitudinal Study of Parents and Children - A resource for COVID-19 research: Questionnaire data capture November 2020 – March 2021

“…The update to the datasets obtained from our previous questionnaires [7][8][9] is described here, together with any variables that have been derived using multiple sets of questionnaire data. We also present a brief assessment of the factors associated with returning the fourth COVID questionnaire, but not any of the previous three, in order to explore who these 'new' participants are.…”